Help with buck switching supply

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#1
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This will be my first switching supply, so I want to consult with you guys before I do anything. There are a plethora of manufacturer and devices from TI and LT and it's got me a little overwhelmed.

This is what I need:

Input from 9-32 VDC
Output of 3.3V
Output current 500mA maximum

There is a potential for a lot noise on the incoming supply as it will be powered by industrial equipment with an alternator and other weird devices on it (not sure if this matters in the selection). The switcher will be powering a uC and a 900 MHz wireless radio.

I'm also a little lost on what switching frequencies I should use and am trying to find a device with a minimal amount of external support components. Can anyone help me with a device that might be nice to work with for a switching newb?

Chief Tinkerer

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Recom (and others) have the solution to your needs:

http://www.recom-international.c...

As for incoming 'noise', a common mode choke and some capacitance should take care of most issues.

Switchers are easy to get wrong and can cause you many problems.

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Murata 7803SR-C, for instance.
Plus automotive grade input filter.

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MC34063?? will work up to 40V input 1.5A sw transistor

regards
Nachus

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Kartman wrote:
Recom (and others) have the solution to your needs:

http://www.recom-international.c...

As for incoming 'noise', a common mode choke and some capacitance should take care of most issues.

Switchers are easy to get wrong and can cause you many problems.

Well that is slick. I'm very comfortable in the LDO world, but I want to get comfortable with switchers. I'm going to go your route for this project and experiment with some switchers when I have some time. The Recom device is not near as expensive as I thought it would be.

Any good leads to datasheet where I can make a nice input protection filter? Something a little more robust than a low-pass with some clamps?
Thanks

Chief Tinkerer

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Quote:
a nice input protection
should be much mrer robust; for instance, see:

http://www.vishay.com/docs/88490...

http://www.vishay.com/docs/49863...

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Alright, so....I've modified the design by including some relays and now my maximum power consumption is close to 800mA. I can't seem to find any of those nifty RECOM regulators that are capable of that kind of output. Any more ideas?

Chief Tinkerer

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nachus001 wrote:
MC34063?? will work up to 40V input 1.5A sw transistor

regards
Nachus

Low cost, well known, not as efficient as newer SwichedModeRegulators though .... but I found it a pretty good suggestion :)

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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LT1073 is a nice and modern one, can handle up to 2 or 3A IIRC

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Quote:
Input from 9-32 VDC
Output of 3.3V
Output current 500mA maximum

I would expect current increase could be handled by a separate regulator just for current hungry addons. It's smart solution because of splitting supply circuits and more flexible power management, especially for relays and alike.

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For a first time switcher design, I highly recommend using Linear Technology parts - for the simple reason that LTSpice is invaluable to see circuit behavior. While you can port non-Linear Technology component pspice models into it, it's easier just to use the LT macromodels. Also, Linear makes some really good switchers - both integrated and discrete switch variants.

Use the parametric search on LT's site to get exactly what you need, or call up your local FAE (call the 800 number on the website, and they will direct you to your FAE). LT's FAEs are usually really good at helping you select the best product for your design. I recently developed a 5V buck circuit around a LT device. However, after spending half an hour on the phone w/ an FAE, I ended up re-doing the design w/ a device that was much better for my precise application.

If you want to delve into practical design theory and applications (rather than more esoteric "Power Supply Theory", Christophe Basso's Switch Mode Power Supplies is phenomenal.

Edit: if you have access to Pspice, the above argument is invalid....

Science is not consensus. Science is numbers.

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triden,
What type of test equipment do you have? How will you validate proper circuit operation? A good O-scope (preferably with differential probes) and a DC Current probe are essential. An Electronic Load is also a big help.